1. Field of the Invention
The present invention relates to data transmission and particularly to a method and means for establishing an outgoing connection from terminal equipment to a base station in a data transmission system. The invention is advantageously applicable to wireless local loop (WLL) systems.
2. Description of the Prior Art
In data transmission systems, the outgoing connection is usually established by a connection code, such as a telephone number. In a fixed line telephone network, each digit of the number is directly transmitted to the exchange as the dialling proceeds. The dialled numbers are analysed in the exchange, and a connection is established right after the dialled sequence has been detected to be an existing telephone number.
Typically, in cellular systems, dialling is done locally. The number is dialled on the keypad and, once the dialling has been completed, a special SEND key is pressed to transmit the dialled number information to the system for analysis.
Terminal equipment used in wireless local loop (WLL) networks include a telephone which can be linked to the public telephone network and a transceiver unit connected to it. Usually, the transceiver unit is linked to the cellular services by radio communication. However, as there is no SEND key available, one of the problems in the WLL systems has been how to decide, when the dialling has been accomplished.
A previously known solution is to use a special end character, which tells the dialling has been completed. A special key character is such a character (e.g.# or *) which is normally not used for dialling. Pressing of the special key tells the terminal that the dialling has been completed, and the number can be transmitted to the base station of the data transmission system. A disadvantage of this solution is, however, that the dialling procedure differs from the one used in conventional fixed networks, and thus the user has to master several different dialling procedures.
Another prior art solution has been to use time supervision. According to this, the elapsed time starting from the last dialled digit is counted, and after a predetermined time, the dialling is supposed to have been completed and the dialled sequence of digits is transmitted to the base station as the connection code.
However, the problem with time supervision is the considerable additional delay needed for the establishment of the connection. This delay is summarized with the time that the system needs to establish the connection. Together, these time delays can become too long compared with the ones needed in a conventional fixed network, where the time elapsed after the dialling of the sequence of digits can be very short. This problem can be diminished by shortening the predetermined delay time. This, however, leads to other problems. Namely, the dialling procedure is not always a constantly ongoing process; e.g. a telephone catalogue may be consulted at the same time for numbers not yet dialled, which may cause a pause of several seconds. If this pause is interpreted as the completion of the dialling procedure, the terminal equipment sends an incomplete telephone number to the base station, and the establishment of the connection fails.
Prior art solutions for realization of WLL systems have more closely been described e.g. in the following patent publications: [1] U.S. Pat. No. 4,658,096; [2] U.S. Pat. No. 4,737,975; [3] U.S. Pat. No. 4,775,997, and [4] U.S. Pat. No. 4,922,517.